Modular stator for axial flux electric machines and methods of assembling the same

ABSTRACT

A stator module pack for an axial flux electric machine is provided. The stator module pack includes a housing for attachment to a stator base and a plurality of stator modules attached to the housing. Each stator module includes a core having at least one winding disposed thereon. A plurality of stator module packs is coupled to a stator base to form a stator of the axial flux electric machine.

BACKGROUND

The field of the disclosure relates generally to axial flux electricmachines, and more specifically, modular stator assemblies for axialflux electric machines.

One of many applications for an electric motor is to operate a pump or ablower. The electric motor may be configured to rotate an impellerwithin a pump or blower, which displaces a fluid, causing a fluid flow.Many gas burning appliances include an electric motor, for example,water heaters, boilers, pool heaters, space heaters, furnaces, andradiant heaters. In some examples, the electric motor powers a blowerthat moves air or a fuel/air mixture through the appliance. In otherexamples, the electric motor powers a blower that distributes air outputfrom the appliance.

A common motor used in such systems is an alternating current (AC)induction motor. Typically, the AC induction motor is a radial fluxmotor, where the flux extends radially from the axis of rotation.Another type of motor that may be used in the application describedabove is an electronically commutated motor (ECM). ECMs may include, butare not limited to, brushless direct current (BLDC) motors, permanentmagnet alternating current (PMAC) motors, and variable reluctancemotors. Typically, these motors provide higher electrical efficiencythan an AC induction motor. Some ECMs have an axial flux configurationin which the flux in the air gap extends in a direction parallel to theaxis of rotation of the rotor.

At least some known axial flux motors include a rotor with a pluralityof permanent magnets and a stator with an annular back iron. The backiron includes a plurality of magnetic teeth formed on the back ironhaving electrically conductive windings disposed thereon. Unlike radialflux motors in which the rotor is positioned within the stator (or viceversa), the rotor and stator are positioned adjacent each other in aface-to-face configuration. The electromagnetic teeth are annularlydisposed around the stator and extend axially towards the permanentmagnets from a back iron that couples the teeth to each other. However,these known axial flux motors typically require customized componentsand costly equipment to manufacture motors with different operatingcharacteristics (e.g., motor size, torque, speed, number of poles,etc.). In addition, maintenance on the components of these motors may bedifficult to perform without replacing the entire rotor or stator.

BRIEF DESCRIPTION

In one aspect, a stator module pack for an axial flux electric machineis provided. The stator module pack includes a housing and a pluralityof stator modules attached to the housing. The housing is attachable toa stator base of the axial flux electric machine. Each stator moduleincludes a core having at least one winding disposed thereon.

In another aspect, a stator for an axial flux electric machine isprovided. The stator includes a stator base and at least one statormodule pack attached the stator base. The stator module pack includes ahousing and a plurality of stator modules attached to the housing. Eachstator module includes a core having at least one winding disposedthereon.

In yet another aspect, a method of assembling an axial flux electricmachine having at least one operational characteristic defined at leastin part by a stator of the axial flux electric machine is provided. Themethod includes determining a number of stator module packs needed toproduce a stator for an axial flux electric machine having at least oneoperational characteristic, determining a radius of the stator based atleast in part on the determined number of stator module packs, andattaching the determined number of stator module packs to a stator baseselected based at least in part on the determined radius. Each statormodule pack includes a housing and a plurality of stator modules. Eachstator module includes a core having at least one winding disposedthereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary axial flux electricmachine.

FIG. 2 is an exploded view of the axial flux electric machine shown inFIG. 1.

FIG. 3 is a top plan view of an exemplary rotor that may be used withthe axial flux electric machine shown in FIG. 1.

FIG. 4A is a perspective view of an exemplary rotor module that may beused with the rotor shown in FIG. 3.

FIG. 4B is an exploded view of the exemplary rotor module shown in FIG.4A.

FIG. 5 is a perspective view of an exemplary flux guide with an extendedlength that may be used with the rotor shown in FIG. 3.

FIG. 6 is a perspective view of an exemplary flux guide with an extendedwidth that may be used with the rotor shown in FIG. 3.

FIG. 7 is a perspective view of an exemplary flux guide with an extendedlength and width that may be used with the rotor shown in FIG. 3.

FIG. 8 is a perspective view of an exemplary flux guide for a pluralityof permanent magnets that may be used with the rotor shown in FIG. 3.

FIG. 9 is a top plan view of an example stator with curved stator modulepacks that may be used with the axial flux electric machine shown inFIG. 1.

FIG. 10 is a perspective view of an exemplary stator module pack thatmay be used with the stator shown in FIG. 8.

FIG. 11 is a partial top plan view of an exemplary stator with straightmodule packs that may be used with the axial flux electric machine shownin FIG. 1.

FIG. 12 is a top plan view of an exemplary straight stator module packthat may be used with the stator shown in FIG. 11.

FIG. 13 is a top plan view of an exemplary stator module pack withintegrated electric drive units that may be used with the stator shownin FIG. 8.

FIG. 14 is a perspective view of an exemplary stator with externalelectric drive unit that may be used with the electric machine shown inFIG. 1.

FIG. 15 is a perspective view of an example stator module that may beused with the stator module pack shown in FIG. 9.

FIG. 16 is an exploded view of an example stator module that may be usedwith the stator module pack shown in FIG. 9.

FIG. 17 is a flow diagram of an exemplary method for assembling a statorfor an axial flux electric machine that may be used to assembly themachine shown in FIG. 1.

FIG. 18 is a perspective view of an exemplary partial axial fluxelectric machine.

FIG. 19 is a perspective view of an exemplary stator that may be usedwith the axial flux electric machine shown in FIG. 18.

FIG. 20 is a perspective view of an exemplary twelve slot, 0.55 splitratio stator configuration with alternating tooth segments that may beused with the machine shown in FIG. 1.

FIG. 21 is a perspective view of an exemplary twelve slot, 0.45 splitratio stator configuration with alternating tooth segments that may beused with the machine shown in FIG. 1.

FIG. 22 is a perspective view of an exemplary twelve slot, 0.65 splitratio stator configuration with alternating tooth segments that may beused with the machine shown in FIG. 1.

FIG. 23 is a perspective view of an exemplary twelve slot, 0.75 splitratio stator configuration with alternating tooth segments that may beused with the machine shown in FIG. 1.

FIG. 24 is a perspective view of an exemplary twenty-four slot, 0.45split ratio stator configuration with alternating tooth segments thatmay be used with the machine shown in FIG. 1.

FIG. 25 is a perspective view of an exemplary twenty-four slot, 0.55split ratio stator configuration with alternating tooth segments thatmay be used with the machine shown in FIG. 1.

FIG. 26 is a perspective view of an exemplary twenty-four slot, 0.65split ratio stator configuration with alternating tooth segments thatmay be used with the machine shown in FIG. 1.

FIG. 27 is a perspective view of an exemplary twenty-four slot, 0.75split ratio stator configuration with alternating tooth segments thatmay be used with the machine shown in FIG. 1.

DETAILED DESCRIPTION

The systems and methods described herein relate generally to axial fluxelectric machines, and more specifically, to modular assemblies foraxial flux electric machines. As used herein, an “axial flux electricmachine” is a motor or generator that uses axial flux to generate apower output (mechanical power output for the motor and electrical poweroutput for the generator).

FIG. 1 is a cross-sectional view of an exemplary axial flux electricmachine 10. FIG. 2 is an exploded view of axial flux electric machine10. In the example embodiment, electric machine 10 is an electric motor.Alternatively, electric machine 10 may operate as an electric generator.In comparison to radial flux electric machines, axial flux electricmachine 10 has a relatively small axial length. Axial flux electricmachine 10 generally includes a rotor 18, a first bearing assembly 20, asecond bearing assembly 22, and a stator 24.

In the exemplary embodiment, rotor 18 generally includes a rotor base 30coupled to a shaft 32. A plurality of rotor modules 34 are coupled torotor base 30. As described in detail further herein, each rotor module34 includes one or more permanent magnets (not shown in FIG. 1). Rotorassembly 18 is rotatable within housing 16, and more specifically,rotatable within first bearing assembly 20 and second bearing assembly22 about an axis of rotation 36. In the exemplary embodiment, rotor 18is driven by an electronic control (not shown), for example, asinusoidal or trapezoidal electronic control.

Stator 24 includes a stator base 50 and at least one stator module pack52 that is configured to generate axial flux towards rotor modules 34.An air gap 38 is formed between a rotor outer surface and a stator outersurface, and a magnetic flux within machine 10 extends between rotormodules 34 and stator 24 in a direction parallel to axis 36.

FIG. 3 is a perspective view of an example rotor 100 that may be usedwith the axial flux electric machine 10 shown in FIG. 1. Rotor 100includes a rotor base 102, a shaft 104, and a plurality of rotor modules106 attached to rotor base 102. In other embodiments, rotor 100 includesadditional, fewer, or alternative components, including those describedelsewhere herein.

In the example embodiment, rotor base 102 is a circular disk having acircumferential outer edge 108 and an inner edge 110. In otherembodiments, rotor base 102 has a different shape. Rotor base 102 has anouter radius R_(r) and an outer circumference. In the exampleembodiment, rotor base 102 may be fabricated from a non-magneticmaterial, such as plastic, aluminum, and stainless steel. In otherembodiments, rotor base 102 is at least partially fabricated from amagnetic material. Shaft 104 extends through an opening 112 defined byinner edge 110. Shaft 104 may be configured to rotate with rotor base102 to generate mechanical (motor) or electrical (generator) power.Alternatively, shaft 104 may be configured to be stationary such thatrotor 100 generates power without movement of shaft 104. Rotor base 102is configured to rotate in response to magnetic forces associated withrotor modules 106 as described herein.

Rotor modules 106 are disposed on a face surface 103 of rotor base 102such that rotor modules 106 are substantially aligned with stator modulepacks (e.g., packs 52, shown in FIG. 1) on an adjacent stator. In theexample embodiment, ten rotor modules 106 are circumferentially attachedto rotor base 102 proximate outer edge 108 on face surface 103. In otherembodiments, a different number of rotor modules 106 (including one) areattached to rotor base 102. Although rotor modules 106 are shown in asingle row on rotor base 102, it is to be understood that rotor modules106 may be attached to rotor base in multiple rows that are radiallyspaced and/or circumferentially spaced from each other. In certainembodiments, rotor modules 106 are disposed on face surface 103 in anon-uniform configuration (i.e., spacing varies between at least someadjacent rotor modules 106). In at least some embodiments, rotor base102 and/or rotor modules 106 include one or more slots, fasteners, tabs,openings, hooks, and other components to facilitate secure attachment ofrotor modules 106 to rotor base 102. In the exemplary embodiment, rotormodules 106 include fastener openings 107 (shown in FIG. 4B) that areconfigured to align with a corresponding hole (not shown) on rotor base102 and receive a fastener, such as a screw or bolt, to secure rotormodules 106 to rotor base 102. Adjacent rotor modules 106 define an arcthat is similar to an arc defined by outer edge 108. In otherembodiments, rotor modules 106 are attached to rotor base 102 in othersuitable configurations.

FIG. 4A is a perspective view of an example rotor module 106 and FIG. 4Bis an exploded view of the example rotor module 106 that may be usedwith rotor 100 shown in FIG. 3. FIGS. 4A and 4B are collectivelyreferred to herein as FIG. 4. Each rotor module 106 includes a back ironsegment 114 (shown in FIG. 4B) configured to attach to rotor base 102and a plurality of permanent magnets 116 attached to back iron segment114. In the exemplary embodiment, back iron segment 114 includesopenings 107 that are configured to receive a fastener to secure rotormodule 106 to stator base 102. Back iron segment 114 is fabricated froma magnetic material to provide a flux path between magnets 116. Themagnetic material may include, but is not limited to, laminated steel,soft magnetic composite (SMC), ferromagnetic steel, and combinationsthereof.

Rotor module 106 has an inner arcuate length L_(bi) and an outer arcuatelength L_(bo). The outer length L_(bo) is less than the circumference ofrotor base 102 such that multiple rotor modules 106 can be attached to asingle rotor base 102. The lengths L_(bi) and L_(bo) are defined by theradius R_(r) of rotor base 102 and an arc angle of rotor module 106. Insome embodiments, rotor module 106 may be substantially straight suchthat lengths L_(bi) and L_(bo) are substantially linear. Attachingmultiple straight modules 106 around rotor base 102 at different anglesenables modules 106 to approximate an arc around rotor base 102. Thecurvature or arc angle of rotor module 106 is defined by the radiusR_(r) of rotor base 102. Alternatively, the radius R_(r) is determinedbased on the number of rotor modules 106 and the curvature of rotormodules 106. In other embodiments, the arc angle of rotor module 106 isdependent upon a different feature or design parameter of machine 10(shown in FIG. 1).

Magnets 116 are attached to back iron segment 114 in a configurationwhere they are spaced from each other. In other embodiments, magnets 116may be combined together as one or more magnets with a plurality ofpoles. Magnets 116 are secured to back iron segment 114 using anysuitable connection means, such as adhesive, clamps, friction-fit, andother suitable means. In the example embodiment, back iron segment 114includes ten magnets 116. In other embodiments, back iron segment 114includes any suitable number of magnets 116, and in particular, any evennumber of magnets 116. Adjacent magnets 116 have opposite polarities forforming flux paths between magnets 116. With magnets 116 of oppositepolarities and a magnetic back iron segment 114, adjacent rotor modules106 may be electromagnetically separate from each other (i.e., no fluxpaths are provided between adjacent rotor modules 106) and stilloperate. That is, each rotor module 106 is configured to provide acomplete magnet path between a first magnet 116, back iron segment 114,and a second magnet 116 having a polarity opposite the polarity of thefirst magnet 116. In one embodiment, rotor 100 includes the same numberof magnets 116 as the number of windings and/or teeth of an adjacentstator (not shown in FIG. 3). In the exemplary embodiment, permanentmagnets 116 are fabricated from neodymium and are formed in atrapezoid-shape. However, any suitable permanent magnet shape andmaterial may be used that enables electric machine 10 to function asdescribed herein.

In the example embodiment, each rotor module 106 further includes amagnet retainer 120. In other embodiments, rotor modules 106 do notinclude magnet retainer 120. Magnet retainer 120 is fabricated from anon-magnetic material (e.g., plastic). In at least some embodiments,magnet retainer 120 is fabricated from a non-conductive material. Magnetretainer 120 is coupled to rotor base 102 and/or back iron segment 114such that magnet retainer 120 extends axially towards an adjacentstator. In the example embodiment, magnet retainer 120 includes slots122 that are aligned with magnets 116 such that a face surface 124 ofmagnets 116 is exposed. In some embodiments, during assembly of rotormodule 106, magnet retainer 120 is coupled to back iron segment 114prior to installing magnets 116. In such embodiments, slots 122 areconfigured to facilitate aligning magnets 116 on back iron segment 114.In other embodiments, slots 122 are sized and/or shaped to preventmagnets 116 from moving in the axial direction towards the stator and tosecure magnets 116 to back iron segment 114.

In the exemplary embodiment, back iron segment 114 includes a tab 126extending beyond magnet retainer 120 and an opening 128. In at leastsome embodiments, tab 126 and opening 128 are formed by positioning backiron segment 114 out of alignment with respect to guard 120. That is,tab 126 is a portion of back iron segment 114 and opening 128 is definedby guard 120 and the absence of back iron segment 114. Tab 126 isconfigured to be inserted into opening 128 of an adjacent rotor module106 to secure adjacent rotor modules 106 together. In some embodiments,tab 126 and/or opening 128 include hooks, slots for fasteners, and/orother features to facilitate coupling adjacent rotor modules 106together. In other embodiments, back iron segment 114 does not includetab 126 or opening 128. For example, if the length L_(b) of rotor module106 is substantially straight, guard 120 may not include tab 126 andopening 128 due to the angled positions of adjacent rotor modules 106.Alternatively, adjacent rotor modules 106 may be physically separatefrom one another.

Rotor modules 106 are configured to enable a user to design, assemble,and maintain a customized axial flux electric machine. That is, rotormodules 106 may be mass-produced with various curvatures, number ofmagnets, and the like. When the user designs an electric machine, theuser determines a size and shape of the stator as described herein.Based on the determined size and shape of the stator, the userdetermines the size of rotor base 102. Rotor base 102 may have asubstantially similar size and shape as the stator. Alternatively, rotorbase 102 may have a different suitable size and shape. Rotor modules 106are then attached to rotor base 102 to define or approximate an arcsimilar to the arc defined by the stator modules of the stator tofacilitate a flux path between the stator and rotor 100.

During operation, magnetic forces cause magnetic flux to flow frompermanent magnets 116 to the closest stator module (not shown in FIGS. 3and 4). When magnets 116 are not aligned with a stator module, a portionof the available flux may be lost (i.e., the stator module does notcapture all of the available flux). Generally, the more effectively thatavailable flux that is channeled from permanent magnets 116 and capturedby the stator modules, the more efficient machine 10 operates.Therefore, it is desirable to cause as much flux as possible to becaptured by the stator modules. However, because the plurality ofpermanent magnets 116 are rotating above the stator, magnets 116 are notalways positioned directly over the stator modules to provide for astraight flow path of flux from magnets 116 to the modules.

In some known electric machines, the flux changes magnitude within thebody of the magnets to reach the stator modules. The change in fluxmagnitude creates eddy currents, which may cause heat generation andtorque losses, potentially resulting in a reduction in operatingefficiency of the machine. Additionally, the heat produced by the eddycurrents may cause demagnetization of the magnets and/or failure of anadhesive used to retain the magnets within the rotor, which may causethe magnets to disengage from the rotor, resulting in failure of themachine. Furthermore, in some known machines, some flux may not bechanneled to the stator and may leak to a different part of the rotor orthe stator. Such leakage may not only cause a reduction in torquegeneration, thereby making the machine potentially less efficient, butalso may cause an undesirable dynamic force distribution inside themachine that may lead to increased noise production and vibration.

In at least some embodiments, rotor 100 includes a flux guide (not shownin FIGS. 3 and 4) for one or more magnets 116 to facilitate reduced eddycurrents, noise, and vibrations. The flux guide (also sometimes referredto as a “magnet shim” or a “magnet tip”) is positioned on magnet 116such that the flux guide is between magnet 116 and an adjacent stator.In some embodiments, the flux guide is secured to magnet 116 (e.g.,using an adhesive). In the example embodiment, the flux guides aremanufactured from an isotropic SMC material, such as Somaloy® (availablefrom Höganäs AB of Höganäs, Sweden). In other embodiments, the fluxguides are manufactured from a different magnetic material. In theexemplary embodiment, the flux guides have a thickness of approximately2 millimeters. Alternatively, the flux guides may have any thicknessthat enables machine 10 to function as described herein. An air gap(e.g., air gap 38, shown in FIG. 1) is defined between the flux guideand the stator.

The flux guide has a shape and a size that enables the flux guide to atleast partially cover face surface 124 of magnet 116. In the exampleembodiment, the flux guide is configured to extend beyond the majorityof the edges of surface 124 of magnet 116 to which it is attached todirect flux from magnets 116 to the stator and back. For example, theflux guides may have a width and a length that extends beyond acorresponding width and length of magnet 116. This overhang facilitatesadditional degree(s) of freedom when optimizing noise, cost, andefficiency of rotor 100 and the configuration of magnets 116. The shapeof the flux guide is any suitable shape to enable machine 10 to functionas described herein. In one example, the shape of the flux guide issubstantially similar to the shape of magnet 116. In another example,the shape of the flux guide is different from the shape of magnet 116.As used herein with respect to flux guides, a “different shape” incomparison to a first shape may include another geometrical shape (e.g.,cylinder, cube, etc.) different from the first shape or the samegeometrical shape as the first shape but with different lengths, widths,arcs, angles, and so forth. For example, if the flux guide and magnet116 are both trapezoids having different arc angles, the flux guide andmagnet have different shapes. In certain embodiments, rotor 100 mayinclude at least two different shaped or sized flux guides to functionas described herein.

In some embodiments, the adjacent flux guides define an arcsubstantially similar to the arc defined by rotor modules 106. Forexample, if rotor modules 106 have a substantially straight length L_(b)and are attached to rotor base 102 at different angles to approximate anarc around rotor base 102, the flux guides may be coupled to rotormodules 106 to define a substantially uniform annular arc around rotorbase 102. In certain embodiments, each flux guide is positioned on morethan one magnet 116 and extends to or beyond the edges of surface 124for each magnet 116 to which it is attached.

During operation of machine 10, the flux generated by magnet 116 ischanneled to one or more stator modules by a respective flux guide. Whenmagnet 116 is not aligned with a stator module, the flux guide steers orchannels portions of the flux from magnet 116 to nearby stator modules.By channeling flux to the stator modules through the flux guides toreduce the change in flux magnitude within magnets 116, the formation ofeddy currents within magnets 116 is substantially reduced or otherwiseeliminated.

Substantially all of the flux generated by magnets 116 is channeled toand captured by the stator modules, resulting in higher torqueproduction and more efficient operation of machine 10. Additionally, theflux guides facilitate reducing the leakage of flux to components ofmachine 10 other than the stator modules because substantially all ofthe flux is captured by the stator modules. The reduction of fluxleakage reduces the dynamic force distribution within machine 10 and,therefore, reduces the generation of endemic noise and vibrations.Furthermore, the reduction or elimination of eddy currents withinmagnets 116 reduces the amount of heat generated by machine 10, whichresults in higher efficiency and facilitates retention of magnets 116within rotor 100.

In at least some embodiments, the flux guides are extended beyond theedges of magnets 116 to provide a potential leakage path for flux. Theleakage path is insignificant for small air gaps between the flux guideand a stator module (i.e., when the stator module is directly alignedwith the flux guide), but increases the rate of flux reduction into aparticular stator module as the air gap increases.

FIGS. 5-8 are perspective views of some example flux guideconfigurations that may be used with rotor 100 shown in FIG. 3. Inparticular, FIG. 5 is a perspective view of a first flux guide 140having an extended length L_(f), FIG. 6 is a perspective view of asecond flux guide 150 having an extended width W_(f), FIG. 7 is aperspective view of a third flux guide 160 having an extended lengthL_(f) and width W_(f), and FIG. 8 is a perspective view of a fourth fluxguide 170 positioned on a plurality of permanent magnets 172. Fluxguides 140, 150, 160, and 170 are shown for descriptive purposes only,and are not meant to limit the configuration of flux guides as describedherein.

With respect to FIGS. 5-7, each flux guide 140, 150, and 160 ispositioned on a respective magnet 116. In particular, flux guides 140,150, and 160 are positioned on face surface 124 of magnet 116. In theexemplary embodiments, flux guides 140, 150, and 160 have an arcuatetrapezoidal shape similar to the shape of magnet 116. In anotherembodiment, magnets 116 are shaped as a portion or section of an annulusdefined by all of magnets 116. In other embodiments, flux guides 140,150, and 160 have a different shape and are not required to be the sameshape as magnet 116. Magnet 116 has an arcuate inner edge 132, anarcuate outer edge 134, a first side edge 136, and an opposing secondside edge 138. Face surface 124 is defined by edges 132, 134, 136, and138. Arcuate inner edge 132 has an arc length less than the arc lengthof outer edge 134 such that face surface 124 tapers inwardly. In theexemplary embodiment, when rotor 100 is assembled, inner edge 132 ofmagnet 116 is positioned towards inner edge 110 of rotor base 102 andouter edge 134 of magnet 116 is positioned towards outer edge 108 ofrotor base 102 (each shown in FIG. 3). Side edges 136 and 138 arepositioned towards adjacent magnets 116 on rotor 100.

With respect to FIG. 5, flux guide 140 includes a magnet surface 141, anarcuate inner edge 142, a gap surface 143, an arcuate outer edge 144, afirst side edge 146, and a second side edge 148. Magnet surface 141 ispositioned adjacent face surface 124 of magnet 116. Gap surface 143 isoriented towards a stator (not shown in FIG. 5) during operation. Inneredge 142 is smaller than outer edge 144 such that magnet surface 141 andgap surface 143 taper inwardly. The arc length of inner edge 142 is lessthan the arc length of outer edge 144. Flux guide 140 has a maximumwidth W_(f) defined between first and second side edges 146 and 148 thatis substantially similar to a width of magnet 116. The length L_(f) offlux guide 140 is defined between inner edge 142 and outer edge 144 andextends beyond inner and outer edges 132 and 134 of magnet 116 such thatflux guide 130 covers the entirety of face surface 124. In someembodiments, flux guide 140 may extend beyond only one of inner edge 132and outer edge 134 of magnet 116. In at least some embodiments, fluxguide 140 is tapered such that an air gap (e.g., air gap 38, shown inFIG. 1) between flux guide 140 and a stator tooth at inner edge 142 isdifferent from an air gap at outer edge 144. The tapered air gapfacilitates balancing flux entering an inner edge and an outer edge of astator tooth to prevent flux from flowing perpendicular to thelaminations of the stator tooth.

With respect to FIG. 6, flux guide 150 includes a magnet surface 151, anarcuate inner edge 152, a gap surface 153, an arcuate outer edge 154, afirst side edge 156, and a second side edge 158. Flux guide 150 andmagnet 116 have different arc angles. Magnet surface 151 is positionedadjacent face surface 124 of magnet 116. Gap surface 153 is orientedtowards a stator (not shown in FIG. 6) during operation. Flux guide 150has a length L_(f) defined between inner and outer edges 152 and 154that is substantially similar to a length of magnet 116. The maximumwidth W_(f) of flux guide 150 is defined between first and second sideedges 156 and 158 and extends beyond first and second side edges 136 and138 of magnet 116 such that flux guide 130 covers the entirety of facesurface 124. In some embodiments, flux guide 150 may extend beyond onlyone of first side edge 136 and second side edge 138 of magnet 116. In atleast some embodiments, flux guide 150 is tapered between inner edge 152and outer edge 154 to provide a different size air gaps at each edge152, 154.

With respect to FIG. 7, flux guide 160 includes a magnet surface 161, aninner edge 162, an air gap surface 163, an outer edge 164, a first sideedge 166, and a second side edge 168. Magnet surface 161 is positionedadjacent to face surface 124 of magnet 116. Air gap surface 163 isoriented towards a stator (not shown in FIG. 7) during operation. Fluxguide 160 has a length L_(f) defined between inner and outer edges 162and 164 and a width W_(f) defined between first and second side edges166 and 168. The length L_(f) and width W_(f) of flux guide 160 extendsbeyond the length and width of magnet 116 to cover the entirety of facesurface 124. In at least some embodiments, flux guide 160 is taperedbetween inner edge 162 and outer edge 164 to provide a different sizeair gaps at each edge 162, 164.

With respect to FIG. 8, flux guide 170 is similar to flux guides 140,150, and 160 and includes similar components. Flux guide 170 ispositioned on a plurality of cylindrical magnets 172. Magnets 172 have aface surface 174 that is adjacent to magnet surface 171 of flux guide170, a back iron surface 176, an edge portion 178 and a radius R_(mg)that is less than the length L_(f) and width W_(f) of flux guide 170.Edge portion 178 extends between face surface 174 and back iron surface176. Magnets 172 only have a single edge portion 178 because of theircylindrical shape. However, in other embodiments, magnets 172 may have aplurality of edge portions if magnets 172 have a different shape, suchas a rectangle or a trapezoid. Although magnets 172 are shown havinguniform shapes and sizes, it is to be understood that any suitablecombinations of shapes and sizes can be used for magnets 172.Irrespective of the size and shape of magnets 172, flux guide 170 isconfigured to cover face surface 174 of each and every magnet 172. In atleast some embodiments, flux guide 170 is configured to extend beyondmagnets 172 in at least one direction.

FIG. 9 is a top plan view of an example stator 200 that may be used withthe axial flux electric machine 10 shown in FIG. 1. Stator 200 may be amultiphase stator (e.g., three phases) or a single phase stator thatproduces flux in the axial direction (i.e., parallel to axis of rotation36 shown in FIG. 1). Stator 200 includes a stator base 202 and aplurality of stator module packs 204 attached to stator base 202. Inother embodiments, stator 200 includes additional, fewer, or alternativecomponents, including those described elsewhere herein. FIG. 10 is apartial exploded view of a curved stator module pack 204.

With respect to FIGS. 9 and 10, stator base 202 has a circular shape andincludes an outer edge 206 that defines a circumference and a radiusR_(s) of base 202. In other embodiments, stator base 202 may be adifferent shape or size. The shape and/or size of stator base 202 may bedetermined based on an intended use of the axial flux machine withstator 200 and/or the number of stator module packs to be installed onstator base 202. In the example embodiment, stator base 202 isfabricated from a material or combination of materials having a suitablerigidity and strength to support stator module packs 204. In someembodiments, stator base 202 is a non-magnetic material or combinationof materials, such as a plastic or non-magnetic metal. Alternatively,stator base 202 may be fabricated from a magnetic material. Stator base202 may include or more mounting points (not shown) for coupling statormodule packs 204, stator drivers (not shown in FIG. 8), and/or a rotorto stator base 202. In the exemplary embodiment, stator module packs 204are evenly distributed around stator base 202 in a complete, uniformannulus configuration. In other embodiments, stator module packs 204 maybe connected to stator base 202 in a non-uniform configuration (i.e.,spacing varies between at least some adjacent stator module packs 204).

Stator module packs 204 include a housing 208 and one or more statormodules 210 attached to housing 208. Housing 208 includes an innerradial wall 212, an outer radial wall 214, a first end wall 216, asecond end wall 218, a face surface 220, and a base surface 222. Whenstator 200 is assembled, face surface 220 is oriented to face the rotorand base surface 222 is oriented towards stator base 202. The walls andsurfaces of housing 208 define an enclosed volume 224 for stator modules210. In FIG. 10, face surface 220 is removed from housing 208 to viewthe interior of volume 224. In some embodiments, face surface 220includes a plurality of teeth openings 221 that are aligned with statormodules 210 to facilitate transmission of axial flux to the rotor. Inother embodiments, face surface 220 does not include teeth openings 221.Housing 208 has an inner arcuate length L_(mi) extending along innerradial wall 212, an outer arcuate length L_(mo) extending along outerradial wall 214, and a width W_(m) extending from inner radial wall 212to outer radial wall 214. The inner length L_(mi) is less than the outerlength L_(mo). Although housing 208 is shown as having arcuate lengthsL_(mi) and L_(mo), in some embodiments, housing 208 may be substantiallystraight to facilitate attaching stator module packs 204 arounddifferent stators having different circumferences of stator base 202. Insuch embodiments, inner and outer lengths L_(mi) and L_(mo) may besubstantially similar to each other. In other embodiments, housing 208has a different shape to facilitate positioning stator modules 210 in adifferent configuration. For example, although stator modules 210 areshown in a single arc, in some embodiments, housing 208 is configured tofacilitate two-dimensional configurations of stator modules 210 and/orradial configurations.

In the example embodiment, housing 208 is a rigid material to provideprotection to stator modules 210 (not shown in FIG. 9). In otherembodiments, housing 208 is at least partially flexible to enable statormodule pack 204 to be adjusted to a particular curvature or shape, andthus enabling stator module packs 204 to be used for variousconfigurations of stator 200. For example, inner radial wall 212, outerradial wall 214, face surface 220, and base surface 222 may includeflexible joints and rigid segments to facilitate adjustment of statormodule pack 204. Alternatively, stator module packs 204 may be formedwith a rigid housing 208 having a predetermined arc angle or curvature.

Housing 208 includes one or more mounting points 225that align with acorresponding mounting point on stator base 202. Mounting points 225 areconfigured to receive a fastener (e.g., screw, bolt, dowel, clamp, etc.)to secure stator module packs 204 to stator base 202. Additionally oralternatively, housing 208 includes one or more tabs, slots, latches,adhesive, and/or other component that engages stator base 202 to securestator module packs 204 to stator base 202.

In the example embodiment, stator module packs 204 are annularlyattached to stator base 202 adjacent to each other and outer edge 206.In some embodiments, at least a portion of stator module packs 204 areseparated from one or more adjacent packs 204 to define a pack gap (notshown) between adjacent packs 204. The pack gap may be any size,including less than inner arcuate length L_(mi) of housing 208 andgreater than outer arcuate length L_(mo) of housing 208. Alternatively,adjacent stator module packs 204 contact each other after assembly ofstator 200. Stator module packs 204 are curved to define an arc thataligns with outer edge 206 of stator base 202. In other embodiments,housings 208 have arcuate lengths L_(mi) and L_(mo) that are defined bythe radius R_(s) and an arc angle such that the curvature of housings208 aligns with the curvature of outer edge 206. Alternatively, statormodule packs 204 may be attached to stator base 202 in a differentconfiguration. In one example, stator module packs 204 are radiallyattached to stator base 202.

In the example embodiment, each stator module pack 204 includes sixstator modules 210. In other embodiments, stator module pack 204 mayinclude a different number of stator modules 210 (including one). In oneexample, each stator module pack 204 includes three stator modules 210.In another example, stator 200 includes one or more stator modules 210with a different number of stator modules 210. Stator modules 210 arepositioned adjacent to each other within housing 208 such that a modulegap 226 is defined between each adjacent stator module 210. Statormodules 210 are positioned in a single line along the length L_(m) ofhousing 208. In the example embodiment, stator modules 210 arepositioned in a single, substantially straight line between the innerand outer arcuate lengths L_(mi) and L_(mo) of housing 208 within volume224. In other embodiments, stator modules 210 are positioned in adifferent configuration within volume 224. Alternatively, stator modulepacks 204 may not include modules 210. Rather, in such embodiments,stator module packs 204 include a single portion of a stator core (notshown) that has a plurality of stator teeth.

In the example embodiment, stator modules 210 are attached to a circuitboard 228 that extends along a portion of housing 208 within volume 224.Circuit board 228 is configured to mechanically secure modules 210together and to electrically couple each module 210 to one or moreinputs and outputs (e.g., power input, drive signals, etc.). In someembodiments, circuit board 228 electrically couples at least a portionof modules 210 together. Alternatively, circuit board 228 mayelectrically isolate each module 210 from each another.

FIG. 11 is a partial plan view of an exemplary stator 200 with straightstator module packs 230. FIG. 12 is a top plan view of the exemplarystraight stator module pack 230. Stator module pack 230 is similar tostator module pack 204 and, in the absence of contrary representation,includes similar components.

With respect to FIGS. 11 and 12, each stator module pack 230 includes ahousing 232 with a substantially straight length L_(ms). A face surface(not shown) of housing 232 is removed for clarity purposes. Statormodule packs 230 are coupled to stator base 202 at different angles toform a group of linear packs 230 that approximate an arc a_(r) matchingor similar to an arc defined by the radius R_(s) and outer edge 206(i.e., the circumference). As the number of packs 230 increases, theangle between adjacent packs 230 decreases such that the arc a_(r)substantially matches the arc defined by the radius R_(s) and outer edge206. The straight module packs 230 enable a user to install statormodule packs 230 on a variety of stator bases 202 having different sizesand shapes, thereby increasing the flexibility and modularity of theuser's design options for an axial flux electric machine.

With respect again to FIGS. 9 and 10, each stator module pack 204 iselectrically coupled to one or more electric drive units (not shown inFIGS. 9 and 10). As used herein, “electrically coupled” components donot require electricity or current to actually be present between thecomponents, but are coupled such that when current is present, thecurrent is transferred between the electrically coupled components. Theelectric drive units are coupled to a power source and include one ormore drive circuits. The drive circuits include, for example, inverters,rectifiers, transformers, and the like that facilitate control of theperformance of machine 10 (shown in FIG. 1). In some embodiments, theelectric drive units are in communication with a controller (not shown).In other embodiments, the electric drive units include an integratedcontroller. The electric drive units are configured to generate a drivesignal to stator module pack 204 to cause axial flux to be generated,thereby facilitating movement of an adjacent rotor. The drive signal forat least some stator modules 210 are synchronized together to increasethe torque, speed, and/or efficiency of the rotor. The drive signal maybe mono-phase or multi-phase. In one example, three electric drive unitsoperate together to generate a three-phase drive signal. In anotherexample, one electric drive unit generates a three-phase drive signal.

In some embodiments, one or more electric drive units are electricallycoupled to each and every stator module pack 204 on stator 200. In otherembodiments, one or more electric drive units are electrically coupledto a subset of stator module packs 204 (i.e., at least one pack 204) ofstator 200. In such embodiments, the electric drive units arecommunicatively coupled to each other to facilitate synchronizing thedrive signals together. In some embodiments, each stator module pack 204is electrically coupled to a single electric drive unit. In otherembodiments, each stator module pack 204 includes an electric drive unitfor each phase of pack 204. For example, if pack 204 has three phases,three electric drive units are electrically coupled to each pack 204.

In some embodiments, the electric drive units are attached adjacentstator module packs 204. For example, the electric drive units may beattached to stator base 202 proximate packs 204. In other embodiments,the electric drive units are integrated within the stator modules packs204 such that each pack 204 acts as a self-contained stator. That is, itis possible to operate machine 10 using only a single stator module pack204. Packs 204 are electromagnetically independent of each other (i.e.,each pack 204 generates and completes a flux path by itself) in at leastsome embodiments, and therefore may be operated without synchronizingwith the other packs 204.

FIG. 13 is a top plan view of an example stator module pack 204 thatincludes a plurality of integrated electric drive units 300. Statormodule pack 204 is substantially similar to pack 204 shown in FIG. 10and includes similar components.

Drive units 300 are electrically coupled to a power input 302 and atleast a portion of stator modules 210. Connections with stator modules210 are not shown in FIG. 13 for clarity purposes. Power input 302 ispower provided by an external power source (e.g., a battery or utilitypower grid). In certain embodiments in which machine 10 (shown inFIG. 1) is a generator, power input 302 is power generated by machine10. Drive units 300 generate a drive signal based on power input 302 andprovide the drive signal to stator modules 210. In one embodiment, thedrive signal is a single phase power signal. Alternatively, the drivesignal may be a multiphase power signal (e.g., three-phase power). Inthe example embodiment, each drive unit 300 is coupled to two respectivestator modules 210 to provide a different phase of the drive signal suchthat a cumulative three-phase drive signal is provided to stator modules210. That is, one electric drive unit 300 generates a drive signalhaving a first phase, a second drive unit 300 generates a drive signalhaving a second phase, and a third drive unit 300 generates a drivesignal having a third phase. The drive signals cause stator modules 210to provide flux paths for flux from a rotor (not shown in FIG. 13) androtate the rotor.

In the example embodiment, drive units 300 includes at least a drivecircuit 306 and a controller 308. In some embodiments, each drive unit300 includes a plurality of drive circuits 306, where each drive circuit306 is electrically coupled to a respective subset of stator modules210. Drive circuit 306 is configured to convert at least a portion ofpower input 302 into the drive signal for stator modules 210. Drivecircuits 306 may include an inverter and/or an alternatingcurrent-to-alternating current (AC-AC) converter depending upon thepower input 302. In some embodiments, drive circuit 306 includes othersuitable components (e.g., rectifiers, computer storage devices, etc.)that enable drive units 300 to perform as described herein. In someembodiments, each drive unit 300 includes a plurality of drive circuits306, wherein each drive circuit 306 is coupled to a respective subset ofstator modules 210 to provide the drive signals. In one example, driveunit 300 includes three drive circuits 306.

In the exemplary embodiment, controller 308 includes a processor 310 anda memory device 312. In the exemplary embodiment, controller 308 isintegrated within electric drive unit 300. In other embodiments,controller 308 is implemented in one or more processing devices, such asa microcontroller, a microprocessor, a programmable gate array, areduced instruction set circuit (RISC), an application specificintegrated circuit (ASIC), etc. in communication with electric driveunit 300. Accordingly, in this exemplary embodiment, controller 308 isconstructed of software and/or firmware embedded in one or moreprocessing devices. In this manner, controller 308 is programmable, suchthat instructions, intervals, thresholds, and/or ranges, etc. may beprogrammed for a particular machine 10 and/or an operator of machine 10.Controller 308 may be wholly or partially provided by discretecomponents, external to one or more processing devices.

Controller 308 is communicatively coupled to inverter 306 to controlinverter 306 and adjust the drive signal. That is, controller 308determines the frequency and magnitude of the drive signal based onstored instructions, feedback provided from other components of machine10, and so forth. In one example, controller 308 controls the operationof one or more switches (not shown) within inverter 306 to adjust thedrive signal.

FIG. 14 is a partial perspective view of an exemplary stator 270 thatmay be used with machine 10 shown in FIG. 1. Stator 270 includes astator base 272, a stator module pack 274, and an electric drive unit320. Although only one stator module pack 274 and electric drive unit320 are shown, it is to be understood that stator 270 may include aplurality of stator module packs 274 and electric drive units 320.Stator 270 is substantially similar to stator 200 (shown in FIG. 9)except electric drive units 320 are attached to stator base 272 outsideof stator modules packs 274. Each drive unit 320 is electrically coupledto at least a portion of one stator module pack 274. In otherembodiments, each drive unit 320 is electrically coupled to a pluralityof packs 274. In the exemplary embodiment, drive units 320 are coupledto a surface of base 272 opposite a surface with stator module packs274. In other embodiments, drive units 320 may be attached to base 272and/or packs 274 is any suitable configuration to facilitate operationof machine 10.

FIG. 15 is a perspective view of an exemplary stator module 210 for usein a stator module pack (e.g., pack 204, shown in FIG. 9) and FIG. 16 isan exploded view of the exemplary module 210. Stator module 210 includesa core 240, tooth tips 242, and a bobbin assembly 244. In otherembodiments, stator module 210 includes additional, fewer, oralternative components, including those described elsewhere herein.

In the exemplary embodiment, core 240 is generally U-shaped and includesa pair of teeth 246 connected by a yoke section 248. Alternatively, core240 is a different shape, such as an E-shaped core. In the exemplaryembodiment, core 240 is oriented in a generally axial direction suchthat teeth 246 extend substantially parallel to axis of rotation 36(shown in FIG. 1). In the example embodiment, core 240 is fabricatedfrom a plurality of stacked laminated sheets 241. In other embodiments,core 240 is fabricated from a different material.

In the exemplary embodiment, tooth tips 242 are generally T-shaped andinclude an axial member 250 and a cross member 252. Each cross member252 includes a head surface 254 configured to receive flux from anadjacent rotor. In other embodiments, tooth tips 242 may have adifferent shape or configuration. In the exemplary embodiment, toothtips 242 are fabricated from a plurality of stacked laminated sheets243. In other embodiments, tooth tips 242 are fabricated from SMC oranother magnetic material. Tooth tips 242 include rounded portions 256to reduce noise by reducing the harmonic content of the backelectromagnetic field (EMF) and cogging torque. Tooth tips 242 aregenerally aligned with a corresponding tooth 246 and increase fluxdensity in stator 200 (shown in FIG. 8) and reduce the length of awinding 258 necessary for stator module 210.

Bobbin assembly 244 includes two bobbins 260. That is, bobbin assembly244 includes the same number of bobbins 260 as teeth 246 of core 240.Alternatively, bobbin assembly 244 may include one bobbin 260 positionedon every other tooth 246, and/or one bobbin 260 positioned on yokesection 248. Bobbin 260 includes an opening 262 that closely conforms toan external shape of stator module teeth 246 and tooth tip axial member250. For example, stator module tooth 246 is configured to be positionedat least partially within a first end (not shown) of opening 262, andtooth tip axial member 250 is configured to be positioned at leastpartially within a second end 264 of opening 262.

Assembling stator module 210 includes at least one winding 258 around aplurality of bobbins 260. At least a portion of each tooth 246 of core240 is inserted into a corresponding bobbin opening 262. Tooth tips 242are also coupled to bobbins 260. Specifically, at least a portion ofaxial member 250 is inserted into bobbin opening 262. Once assembled,stator module 210 is placed within a stator module pack 204 for assemblyof a stator.

Using modular packs 204 enables a user to design, assemble and maintaina stator 200 according to particular specifications. That is, packs 204enable creation of a customized axial flux electric machine withoutrequiring expensive, custom manufacturing systems and processes. Rather,the modularity facilitates mass production of packs 204 that can beselected to design a customized motor. In addition, the modular designenables packs 204 to be replaced with relative ease for existingelectric machines.

FIG. 17 is a flow diagram of an example method 270 of assembling anaxial flux electric machine that may be used to assemble a machine thatincludes stator 200 shown in FIG. 8. In particular, the axial fluxelectric machine to be assembled has one or more desired operationalcharacteristics. As used herein, operational characteristics includemechanical and/or electromagnetic properties of the electric machine,such as torque, number of phases, rotations per minute (rpm), electricalcurrent input or output, voltage input or output, power output, and thelike.

To begin, the user determines 272 a number of stator module packssufficient to produce a stator for the axial flux machine that has thedesired operational characteristic(s), such as number of phases, torque,etc. The user determines 274 a radius of the stator based at least inpart on the determined number of stator module packs. In particular, theuser determines 274 the radius to fit each and every stator module in adesired configuration (e.g., an annularly disposed configuration). Inone example, for curved stator module packs, the user calculating an arcangle or arc of the stator modules packs and determines 274 the radiusbased on the calculated arc angle or arc and the number of stator modulepacks. In another example, for straight stator module packs, the radiusis determined 274 based on an approximated curve defined by the straightmodule packs. In other embodiments, the user radius of the stator isdetermined 274 prior to determining 272 the number of stator modulepacks such that the number of stator module packs is determined 272based on the determined radius.

The determined number of stator module packs are attached 276 to astator base selected based at least in part on the determined radiussuch that the stator module packs fit on the stator base. In someembodiments, the radius of the stator base matches the determinedradius. In other embodiments, the radius of the stator base is differentfrom the determined radius. In one example, the radius of the statorbase is greater than the determined radius to include space tolerancebetween the stator module packs. In another example, the radius of thestator base is greater than the determined radius to satisfy one or moreoperational characteristics desired by the user. In a further example,the stator base is selected from one or more predetermined sizes suchthat the radius of the stator base exceeds the determined radius.

With respect again to FIGS. 15 and 16, having a separate core 240 andtooth tips 242 for each stator module 210 facilitates reducedmanufacturing complexity of modules 210. For example, winding 258 can bewound around teeth 246 prior to installing tooth tips 242. Moreover,tooth tips 242 are configured to reduce noise and cogging torque andimprove performance of machine 10 (shown in FIG. 1).

In some embodiments, tooth tips 242 are fabrication from a material orcombination of materials that is different from the material(s) used tofabricate core 240. In one example, core 240 is fabricated fromlaminated steel sheets 241 and tooth tips 242 are fabricated from an SMCmaterial. Using SMC for tooth tips 242 facilitates improved ease ofmanufacturing for modules 210 while maintaining reasonable manufacturingcosts. Moreover, using SMC for tooth tips 242 facilitates improvedthermal performance of stator module 210. That is, SMC-based tooth tips242 dissipate heat at a greater rate than laminated steel, therebyreducing potential thermal issues with modules 210.

FIG. 18 is a partial perspective view of an exemplary axial fluxelectric machine 400 and FIG. 19 is a perspective view of a stator 402of electric machine 400. In the exemplary embodiment, machine 400 is anon-modular electric machine. In other embodiments, machine 400 may beconfigured to be modular similar to machine 10 (shown in FIG. 1).Accordingly, the features and components described herein may be appliedto machine 10. Machine 400 includes stator 402 and a rotor 404. Rotor404 includes a rotor back iron 406 and a plurality of magnets 408annularly disposed around back iron 406.

Stator 402 includes a stator back iron 410, a plurality of teeth 412that extend towards rotor 404, and a plurality of windings 414 that aredisposed on teeth 412. Stator back iron 410 is shown as a single,circular back iron. However, in other embodiments, back iron 410 has adifferent shape and/or includes a plurality of segments that form backiron 410 collectively. Teeth 412 and magnets 408 are radially alignedwith respect to each other. In the exemplary embodiment, stator 402 isfabricated from a first magnetic material, such as laminated steel. Eachtooth 412 is securely coupled to a respective tooth tip 416 such thattooth tips 416 are between teeth 412 and magnets 408. In the exemplaryembodiment, tooth tips 416 have a substantially planar surface and anarcuate trapezoidal shape. Tooth tips 416 have profiled (e.g., rounded,chamfered, complex, etc.) edges that may be otherwise difficult tomanufacture with laminated steel. In other embodiments, tooth tips 416have a different shape, such as a non-planar shape. In the exemplaryembodiment, tooth tips 416 are fabricated from a second materialdifferent from the first material, such as SMC.

Tooth tips 416 extend beyond one or more edges of teeth 412 toward anadjacent tooth 412 and tooth tip 416. Adjacent tooth tips 416 define anair gap 417 that is smaller than slots 418 defined between the adjacenttooth tips 416. Slots 418 have a substantially constant W_(g) betweeneach pair of adjacent teeth 412. Tooth tips 416 are separate from teeth412 to enable windings 414 to be disposed around teeth 412 with relativeease. That is, windings 414 are inserted within slots 418 to be woundaround teeth 412 without needle winding prior to installing tooth tips416. Tooth tips 416 are coupled to teeth 412 using any suitable means,such as adhesive, fasteners, slots, tabs, and the like. Once coupled toteeth 412, tooth tips 416 define gap 417, which has a width that wouldrequire the use of needle winding to install windings 414 after toothtips 416 are installed.

In some embodiments, a combination of laminated steel and an SMCmaterial may be used to form a stator. Laminated steel includes a stackof thin, flat sheets of steel that are laminated together to form athree-dimensional object, such as a stator tooth. Typically, thelaminated object is a stack of identical stampings that have a fixedcross section in one dimension. This fixed cross section is linearly“extruded” to form a final shape with a constant cross section, therebylimiting the shape of the object. Further, the magnetic properties oflaminated objects are distinctly anisotropic. The laminated materialcarries alternating magnetic flux relatively efficiently in two of thethree dimensions. In particular, the two dimensions defined by the planeof lamination efficiently carry. While the laminated material can carryalternating flux in the third dimension, this results in relatively highlosses due to eddy currents circulating in the plane of lamination.Laminated steel is typically a low-cost magnetic material used inelectric machines. SMC is a relatively expensive magnetic material thatcan be molded into a variety of three-dimensional shapes. SMC materialis magnetically isotropic such that objects made from SMC carry magneticflux in any direction inside the 3D object, with substantiallyidentical, relatively low losses in all directions. SMC has a lowermagnetic performance in comparison to laminated steel, but laminatedsteel may require time-consuming manufacturing and may include smallimperfections between the laminated sheets that affect the magneticperformance of the steel. Electric machine components formed from SMCare fabricated with relatively simple manufacturing processes and do nothave the same imperfection issues as laminated steel. Due to the costand performance difference of laminated steel and SMC, a combination ofthe two materials may be used to form a stator.

FIGS. 20-27 are perspective views of exemplary stator configurations foruse in axial flux electric machines (e.g., machine 10 shown in FIG. 1).In particular, each stator includes a plurality of magnetic laminatedtooth segments 510, a plurality of magnetic moldable tooth segments 512,and a plurality of windings 514. In the exemplary embodiment, eachconfiguration includes an equal number of laminated tooth segments 510and moldable tooth segments 512. Alternatively, the statorconfigurations may include an unequal number of tooth segments 510 and512. Laminated tooth segments 510 and moldable tooth segments 512 havedifferent shapes. In the exemplary embodiment, the different shapesapproximate a solid, thick-walled cylinder when the parts are assembled.In each stator configuration, laminated tooth segment segments 510 andmoldable tooth segments 512 are interleaved such that each laminatedtooth segment 510 is between two moldable tooth segments 512 and eachmoldable tooth segment 512 is between two laminated tooth segmentsegments 510. Each winding 514 is disposed on a respective moldabletooth segment 512.

It is to be understood that other materials beyond laminated steel(including non-laminated materials having suitable characteristics tofunction as described herein) may be used to fabricate laminated toothsegment segments 510. Similarly, moldable tooth segments 512 may befabricated a different material other than SMC, even non-compositematerial. Moreover, the stator configurations shown in FIGS. 20-27 arefor illustrative purposes only, and are not intended to limit the statorconfigurations described herein.

FIG. 20 is a perspective view of an exemplary stator configuration 500.The stator configurations of FIGS. 21-27 are similar to statorconfiguration 500, and therefore include similar components. Statorconfiguration 500 has an inner radius R_(i) and an outer radius R_(o).Laminated tooth segment segments 510 include a tooth tip 520, a toothsection 521, and a yoke section 522. Tooth tip 520 is coupled to toothsection 521 at a first end and includes an inner edge 524 and an outeredge 526. Tooth section 521 extends from yoke section 522. In theexemplary embodiment, tooth tip 520, tooth section 521, and yoke section522 are substantially the same at inner edge 524 and outer edge 526because the laminated sheets that form laminated tooth segment segments510 are substantially identical to each other.

Moldable tooth segments 512 include a tooth tip 530, a tooth section531, and a yoke section 532. Tooth tips 530 are coupled to a first endof tooth section 531 and include an inner edge 534 and an outer edge536. Unlike laminated tooth segment segments 510, tooth tip 530, toothsection 531, and yoke section 532 of moldable tooth segments 512 aresubstantially different at inner edge 534 and outer edge 536. Inparticular, moldable tooth segments 512 are smaller at inner edge 534 incomparison to outer edge 536. Using SMC to fabricate moldable toothsegments 512 facilitates non-uniform three-dimensional shapes, such asthose shown in FIGS. 20-27. Laminated tooth segments 510 and moldabletooth segments 512 are coupled together at a second end opposite thefirst ends coupled to tooth tips 520 and 530. In the exemplaryembodiment, windings 514 are disposed on moldable tooth segments 512 andare positioned between tooth sections 521 and yoke section 531 ofadjacent laminated tooth segment segments 510 and moldable toothsegments 512, respectively.

In the exemplary embodiment, as flux traverses from the top of one toothsegment down within stator configuration 500, the flux turns in either aclockwise or an anticlockwise direction and then comes up via anadjacent tooth segment. The flux will spend some distance in laminatedsteel (i.e., laminated tooth segments 510), and some in SMC (i.e.,moldable tooth segments 512). In an axial flux electric machine, thereis always at least some movement of the flux path in a “radial”direction. The differences in the magnetic properties of laminatedsteel, which is anisotropic, and SMC, which is isotropic, mean that fora substantially “minimum energy” solution for the actual position ofeach path, the flux path will travel close to a straight line in thelaminated steel due to the relatively low permeability of flux movingperpendicularly to the lamination direction, and nearly all of theradial movement of the flux path will take place in the SMC.

Stator configuration 500 is a twelve slot stator configuration with asplit ratio (i.e., the ratio between the diameter of inner edge 534 andthe diameter of outer edge 536) of 0.55. FIGS. 21-23 are perspectiveviews of other twelve slot stator configurations 600, 700, and 800.Unlike stator configuration 500, stator configuration 600 has a splitratio of 0.45, configuration 700 has a split ratio of 0.65, andconfiguration 800 has a split ratio of 0.75. FIGS. 24-27 are perspectiveviews of stator configurations 900, 1000, 1100, and 1200. Statorconfigurations 900, 1000, 1100, and 1200 are twenty-four slot statorconfigurations with split ratios of 0.45, 055, 0.65, and 0.75,respectively.

The foregoing systems and methods facilitate various improvements toaxial flux electric machines. In particular, the foregoing systems andmethods facilitate manufacturing improvements, cost improvements,maintenance improvements, and performance improvements to axial fluxmachines. For example, the modular rotor modules and stator modulespacks facilitate improved design and maintenance flexibility for axialflux electric machines. The modular rotors and stators facilitate highvolume production of the modular components, which may result in reducedmanufacturing costs for each component. Using a combination of laminatedsteel and SMC materials either as separate teeth and tooth tips or asalternating tooth segments facilitate design flexibility and improvedperformance of the electric machines without substantially increasingthe cost of the electric machine.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A stator module pack for an axial flux electricmachine, the stator module pack comprising: a housing configured forattachment to a stator base, wherein said housing comprises a first endwall and a second end wall; and a plurality of stator modulessubstantially enclosed by said housing between said first end wall andsaid second end wall, each stator module comprising a core having atleast one winding disposed thereon.
 2. The stator module pack inaccordance with claim 1, wherein said plurality of stator modules arepositioned adjacent each other in a substantially straight line, whereinsaid housing has a straight length extending between said first end walland second end wall.
 3. The stator module pack in accordance with claim1, wherein said plurality of stator modules are positioned adjacent eachother to define an arc, wherein said housing is curved along the arcfrom said first end wall to said second end wall.
 4. The stator modulepack in accordance with claim 3, wherein the arc is defined by a radiusof the stator base.
 5. The stator module pack in accordance with claim1, wherein said core comprises two teeth, each tooth of said two teethhaving a winding of said at least one winding disposed thereon.
 6. Thestator module pack in accordance with claim 1, wherein said plurality ofstator modules includes six stator modules.
 7. The stator module pack inaccordance with claim 1, wherein said plurality of stator modulesincludes three stator modules.
 8. A stator for an axial flux electricmachine, the stator comprising: a stator base; and at least one statormodule pack attached to said stator base, said at least one statormodule pack comprising: a housing comprising a first end wall and asecond end wall; and a plurality of stator modules substantiallyenclosed by said housing between said first end wall and said second endwall, each stator module comprising a core having at least one windingdisposed thereon.
 9. The stator in accordance with claim 8, wherein saidplurality of stator modules are positioned adjacent to each other in asubstantially straight line, wherein said housing has a straight lengthextending between said first end wall and second end wall.
 10. Thestator in accordance with claim 8, wherein said plurality of statormodules are positioned adjacent to each other to define an arc, whereinsaid housing is curved along the arc from said first end wall to saidsecond end wall.
 11. The stator in accordance with claim 10, whereinsaid stator base has an outer edge curved along the arc.
 12. The statorin accordance with claim 11, wherein said at least one stator modulepack is aligned with said outer edge of said stator base.
 13. The statorin accordance with claim 8, wherein said at least one stator module packincludes a plurality of stator module packs.
 14. The stator inaccordance with claim 13, wherein said plurality of stator module packsare angled relative to each other to approximate an arc defined by anouter edge of said stator base.
 15. A method of assembling an axial fluxelectric machine having at least one operational characteristic definedat least in part by a stator of the axial flux electric machine, themethod comprising: determining a number of stator module packs needed toproduce a stator for an axial flux electric machine having the at leastone operational characteristic, wherein each stator module packcomprises a housing including a first end wall, a second end wall, and aplurality of stator modules substantially enclosed by the housingbetween the first end wall and the second end wall, each stator modulecomprising a core having at least one winding disposed thereon;determining a radius of the stator based at least in part on thedetermined number of stator module packs; and attaching the determinednumber of stator module packs to a stator base selected based at leastin part on the determined radius.
 16. The method in accordance withclaim 15, wherein each of the stator module packs has a substantiallystraight length extending between the first end wall and the second endwall of the housing, and wherein determining the radius of the statorfurther comprises determining the radius of the stator based on an arcapproximated by the stator module packs.
 17. The method in accordancewith claim 15, wherein the stator module packs are curved, and whereindetermining the radius of the stator further comprises determining theradius of the stator based on an arc defined by the stator module packs.18. The method in accordance with claim 17, wherein determining theradius of the stator further comprises determining the arc defined bythe stator module packs based on the determined number of stator modulepacks.
 19. The method in accordance with claim 15, wherein the at leastone operational characteristic includes at least one of a torque value,a motor speed, a number of power phases, an electric current value, avoltage value, and a power output.